The present invention relates to a room temperature curable polyorganosiloxane composition suitable for use as a silicone sealant having a paintable surface.
Among polyorganosiloxane compositions which cure into an elastomer at room temperature, various compositions have been known. Particularly in the construction industry, such polyorganosiloxane compositions are used frequently for various purposes such as glazing of glass plates in sashes, sealing of apertures in outer walls of constructions such as precast concrete and molded aluminum plates and sealing of joints in concrete panels and induced joints. They are known generally as silicone sealants. The demand for them is increasing, since they have excellent weather resistance, durability, heat resistance and low temperature resistance, change in physical properties thereof with temperature is insignificant, deterioration by ozone or ultraviolet rays is only slight and they have good workability. Among such silicone sealants those which are curable to elastomers at room temperature by crosslinking silanol group-terminated polydiorganosiloxanes with an aminoxy group-containing organosilicon compound are particularly important as caulking and sealants for outer walls of constructions, particularly high-storied buildings, and since the above silicone sealants having a low modulus can be obtained easily. The sealant which has a low modulus is capable of absorbing a stress caused by the deformation of the constructions and also by the expansion and contraction of the construction materials.
However, the silicone sealants have a defect in that general organic resin paints or cement paints cannot be adhered thereto because of their poor adhesive receptivity.
On the other hand, outer walls of constructions made of concrete, precast concrete, lightweight concrete and lightweight foamed concrete are often after-coated for the purpose of improving the appearance thereof or imparting water-tightness thereto. Therefore, it is desirable that the surface of the sealant filled in the joints of the outer walls can also be applied with the coating. However, as described above, general paints applied to the surface of silicone sealant have no adhesive receptivity and paint will peel off.
A prior method for indirectly ahering a general paint to the surface of a silicone sealant is comprised of the steps of applying a mixture of (1) a viscous polyorganosiloxane resin solution as a mark component which is obtained by reacting (a) a copolymer comprising triorganosiloxane units and SiO.sub.2 units and having a hydroxyl or alkoxyl group bonded to silicon and (b) a silanol group-terminated polydiorganosiloxane and (2) a filler; which mixture is applied to a surface; drying the mixture and applying a general paint to the surface thereof.
However, this method is not preferred since it comprises complicated steps.
After intensive investigations on silicone sealants to which general paints can be adhered, the inventors have found that if a primary or secondary monohydric alcohol having a carbon-to-carbon triple bond in the molecule is added thereto, the surface of the cured sealant will have adhesive properties and paints can easily be adhered thereto. The present invention has been completed on the basis of this finding.